This invention relates to a graft polymer dispersion prepared by the polymerization of an ethylenically unsaturated monomer or mixtures thereof in a polyahl (hereinafter "polymer polyahl" or "copolymer polyahl"). More particularly, the invention relates to an improved process for preparing said copolymer polyahl, and an improved copolymer polyahl prepared thereby.
In recent years it has been known to prepare polymer dispersions in a polyahl mixture. In such dispersions, a polymer of an ethylenically unsaturated monomer or mixture of monomers is dispersed in a polyahl or mixture thereof. The dispersed polymer is normally grafted to the polyahl through some unsaturation in the polyahl. Such unsaturation is commonly introduced into the polyahl by reaction thereof with a small amount of an unsaturated acid, or acid anhydride such as fumaric or maleic acid, or their anhydrides or more recently, isocyanatoethylmethacrylate (IEM). In these copolymer polyahls, the polyahl makes up a continuous phase into which the copolymer is dispersed as a plurality of small particles.
These copolymer polyahls have found great utility in the production of diverse polyurethanes. In particular, the use of copolymer polyahls in preparing polyurethanes has been found to improve the processability of the polyurethane, as well as physical properties such as load bearing or modulus. It is often desirable to provide a copolymer polyahl with as high a dispersed phase content as possible. However, it has heretofore been difficult to prepare and/or use copolymer polyahl containing more than about 35-40 percent by weight dispersed phase. A high concentration of dispersed phase greatly increases the viscosity of the copolymer polyol. When the viscosity exceeds about 6500 cps, it is usually too viscous to be pumped using conventional urethane molding and/or foaming equipment. With conventional copolymer polyahl, a viscosity of 6500 cps is usually reached at a dispersed phase concentration of 35-40 percent or lower. Even at a lower dispersed phase concentration, it is normally preferred to have a viscosity as low as possible to ease the handling of the copolymer polyahl.
Another problem associated with high dispersed phase concentrations is that the stability of the dispersed phase is greatly reduced as the dispersed phase concentration exceeds about 35-40 percent. At higher dispersed phase concentration (higher solids), the copolymer particles tend to coalesce and phase separate. The phase separation of the copolymer greatly impairs the utility of the copolymer polyahl and polyurethane prepared therewith.
Yet another common disadvantage of conventional copolymer polyahls is that in order to provide a stable copolymer dispersion one must introduce substantial amounts of unsaturation into the polyahl through which to graft the dispersed phase. It is generally easier and cheaper to prepare copolymer polyahl having smaller amounts of unsaturation in the polyahl.
It is known to prepare copolymer polyahls by polymerizing ethylenically unsaturated monomers in the presence of the polyahl and a chain transfer agent. The chain transfer agent is used in the preparation of copolymer polyahls in a manner analogous to the use thereof in conventional polymerizations, that is, to control the molecular weight distribution of the polymer. However, the choice of chain transfer agent has not heretofore been attributed to significant improvements in the properties of the copolymer polyahl. In addition, the use of triiodomethyl compounds in making copolymer polyahls has not heretofore been known.
In view of the aforementioned deficiencies of previously known copolymer polyahls, it would be desirable to provide a copolymer polyahl that exhibits high stability and an acceptable viscosity of a high dispersed phase content, or a lower viscosity at an equivalent dispersed phase content then exhibited by a conventional copolymer polyol.